In Vivo Evidence for Microvascular Oxidative Stress in Spontaneously Hypertensive Rats

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Abstract
The factors that predispose to the accelerated organ injury that accompanies the hypertensive syndrome have remained speculative and without a firm experimental basis. Indirect evidence has suggested that a key feature may be related to an enhanced oxygen radical production. The purpose of this study was to refine and use a technique to visualize evidence of spontaneous microvascular oxidative stress in vivo in the spontaneously hypertensive rat (SHR) compared with its normotensive control, the Wistar-Kyoto rat (WKY). We investigated the effects of adrenal glucocorticoids on the microvascular oxidative stress sequence. The mesentery was superfused with hydroethidine, a reduced, nonfluorescent precursor of ethidium bromide. In the presence of oxidative challenge, hydroethidine is transformed intracellularly into the fluorescent compound ethidium bromide, which binds to DNA and can be detected by virtue of its red fluorescence. The fluorescent light emission from freshly exteriorized and otherwise unstimulated mesentery microvessels was recorded by digital microscopy. The number of ethidium bromide–positive nuclei along the arteriolar and venular walls in SHR was found to be significantly increased above the level exhibited by WKY. The elevation in ethidium bromide fluorescence in SHR arterioles could be attenuated by a synthetic glucocorticoid inhibitor and in rats subjected to adrenalectomy. The administration of glucocorticoids after adrenalectomy by injection of dexamethasone restored the oxidative reaction in SHR arterioles. Treatment with dimethylthiourea and with a xanthine oxidase inhibitor attenuated the superoxide formation. Although a nitric oxide synthase inhibitor ( N G -nitro- l -arginine methyl ester) enhanced the ethidium bromide staining in WKY, it did not affect that in SHR. Our findings suggest an enhancement of spontaneous oxidative stress in the microvascular wall of SHR that appears to be associated with glucocorticoid synthesis.